This project focuses on the psychophysiological differences manifest among the alternate personalities of patients with multiple personality disorder (MPD). The occurrence of psychophysiological differences among alternate personalities in excess of chance levels has been documented for EEG, visual evoked potentials, and measures of autonomic activity including heart rate, respiration, skin temperature, and bilateral galvanic skin response. In most cases these differences significantly exceed those manifest by control subjects who were simulating alternate personalities. In some instances, however, control subjects demonstrate as much variability as MPD patients. Further studies are underway to elucidate the mechanisms of these psychophysiological changes.